The effect of dopants on the morphology, microstructure and electrical properties of transparent zinc oxide films prepared by the sol-gel method

The influence of doping on the morphology, physical and electrical properties of zinc oxide produced by the sol-gel method was examined. Undoped zinc oxide was observed to form relatively porous films. Addition of an Al dopant influenced the sheet resistance, but did not result in a change in morphology, examined by atomic force microscopy when compared to undoped films. In the case of electrical measurements, undoped ZnO films were extremely resistive. A minimum dopant concentration of 2 at.%. Al was required to produce materials which were more conductive, as observed by sheet resistance measurements, which were shown to vary with annealing temperature. The versatile nature of sol-gel processing was demonstrated by selective ink-jet deposition of sol-gel droplets which were annealed to form oxide materials.     

Hybrid manganese oxide films for supercapacitor application prepared by sol-gel technique

Hybrid films were prepared by adding various concentrations of meso-carbon microbeads (MCMB) during sol-gel processing of manganese oxide films. The heat-treated films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, electrochemical performance of the MCMB-added Mn-oxide hybrid coatings was evaluated by cyclic voltammetry (CV) and compared with its unadded counterpart. Experimental results showed that Mn-oxide films exhibited a mixture of Mn₂O₃ and Mn₃O₄ phases. The higher the heat-treatment temperature, the more Mn₂O₃ can be observed. The specific capacitance of the unadded Mn-oxide electrodes is 209 F/g. Because the MCMB particles provide more interfacial surface area for electrochemical reactions, a significant improvement can be noticed by adding MCMB in Mn-oxide coatings. The 300 °C heat-treated hybrid Mn-oxide coating with a Mn/MCMB ratio of 10/1 exhibits the highest value of 350 F/g, showing a ~ 170% increase in specific capacitance.     

溶胶-凝胶工艺和氧化物气敏材料

本文简要地综述了溶胶-凝胶工艺、氧化物气敏材料、以及应用溶胶-凝胶工艺制备氧化物气敏材料等方面的最新进展。近年来,人们已发现许多氧化物半导体材料都具有某种气敏特性,材料中杂质的种类及数量、材料的颗粒度及孔隙度分布、以及薄膜样品的厚度等因素都严重地影响着氧化物半导体的气敏特性。应用溶胶-凝胶工艺制备氧化物气敏材料。不仅操作工艺简单、制备过程温度低;而且所制得的产物纯度高,组分均匀,很容易实现均匀的定量掺杂;此外,用溶胶-凝胶工艺所制得的氧化物材料具有很大的比表面积。因此,溶胶-凝胶工艺在制备氧化物气敏材料方面具有很大的优势,近年来已有不少作者采用此工艺制备出氧化气敏材料。     

Synthesis,characterization and gas sensitivity of MoO<Subscript>3</Subscript> nanoparticles

Nanoparticles of molybdenum oxide were synthesized using the citrate sol-gel method and characterized using scanning electron microscopy and X-ray diffraction techniques. The sensitivity of the material to the presence of various gases was analysed and the particles showed higher sensitivity towards NO₂ gas.     

Preparation and characterization of PLZT thin films by sol-gel processing

The effect of acid catalysts on the sol-gel preparation of ferroelectric lead lanthanum zirconium titanate (PLZT) thin films was studied. High quality thin films were successfully produced by using suitable amounts of the drying control chemical additive formamide and also catalyst acids during the sol-gel processing followed by various annealing conditions. The dielectric constants of the PLZT (8/65/35) thin films produced in this study varied between 540 (100 kHz) for a film annealed at 600 °C for 30 mins to a maximum 870 °C (1 kHz), 700 (100 kHz) for a film annealed at 650 °C for 20 mins.     

Size-controlled synthesis of ZnO nanocrystals from diethylzinc and donor-functionalized alcohols

Nanocrystals of zinc oxide (ZnO) were prepared from diethylzinc and donor-functionalized alcohols, 2-methoxyethanol, 2-ethoxyethanol, and 2-methoxyethoxyethanol by sol-gel processing. The nanocrystals were prepared at room temperature and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Crystal sizes were controlled by the type of utilized donor-functionalized alcohol in which decreased by an increase of the chain length and type of the donor-functionalized alcohol from 16 to 27 nm. The HRTEM and SAED results revealed that the degree of crystallinity decreases with increasing donor-functionalized alcohol chain length. The particle size of the ZnO powders demonstrated high tolerance to heat treatment and grow up to approximately 65 to 80 nm upon calcination at 1000 °C.     

Sol-gel synthesis of lanthanum-gallate-based ceramic coatings

Phase-pure (La_0.9Sr_0.1)(Ga_0.7Fe_0.3)O_{3 ? y} and (Sr_1.8La_0.2)(GaFe)O_5.1 powders with the perovskite and brownmillerite structures have been prepared from salt solutions by sol-gel processing at temperatures from 570 to 870 K. Ceramic coatings up to 100 μm in thickness have been produced by applying suspensions of the sol-gel powders to various substrates. The structure and microstructure of the ceramic coatings have been studied by x-ray diffraction and scanning electron microscopy.     

透明氧化物薄膜的制备及其发展趋势

对近几年透明氧化物薄膜的制备进行了综述，重点介绍了溶胶-凝胶法、电沉积法、水热电化学法和喷雾热解法等方法的制备特点、性能评价以及透明氧化物薄膜的应用领域，并对今后透明氧化物薄膜的制备发展趋势进行了预测。     

Fabrication of TiO2 nanotube film by well-aligned ZnO nanorod array film and sol-gel process

High density TiO₂ nanotube film with hexagonal shape and narrow size distribution was fabricated by templating ZnO nanorod array film and sol-gel process. Well-aligned ZnO nanorod array films obtained by aqueous solution method were used as template to synthesize ZnO/TiO₂ core-shell structure through sol-gel process. Subsequently, TiO₂ nanotube array films survived by removing the ZnO nanorod cores using wet-chemical etching. Polycrystalline anatase TiO₂ nanotube films were ∼ 1.5 μm long and ∼ 100 nm in inter diameter with a wall thickness of ∼ 10 nm.     

Room-temperature crystallization of amorphous films by RF plasma treatment

The crystallization of amorphous thin films was achieved by 13.56 MHz RF (radio frequency) plasma treatment. This crystallization process has a strong advantage that the sample temperature is lower than 120 °C during the plasma treatment even without compulsory cooling and various amorphous films are crystallized after 2 min or so. This treatment works on amorphous films of various materials, independently of the film preparation method and substrate materials. Crystallization has been confirmed on amorphous thin films of sputtered ITO (tin doped indium oxide) deposited on soda-lime glass and PET (polyethylene terephthalate), of sputtered TiO₂ on soda-lime glass, of sol-gel derived TiO₂ on silicon wafer and of sputtered hydrogen-doped silicon on soda-lime glass.The plasma gas pressure was found to be the key parameter in the plasma crystallization process. The appropriate gas pressure depends on the plasma gas species and not on film or substrate materials. A Cu electrode, attached to the backside of the substrate and is electrically floated from the electric ground, was found to enhance the plasma crystallization performance.     

The effect of multi-walled carbon nanotubes/hydroxyapatite nanocomposites on biocompatibility

In the present study, multi-walled carbon nanotubes/hydroxyapatite (MWCNTs/HA) nanocomposites with various MWCNT contents were manufactured by sol-gel processing. The MWCNTs/HA powder was characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman analysis. The results show that the MWCNTs were fully covered with HA nanoparticles and help forming the crystallized hydroxyapatite. In addition, in vitro tests highlighted the excellent biocompatibility of the MWCNTs/HA composite.     

Sol-gel preparation of silica glass

This paper is a preliminary report on the preparation of silica glass containing very low amount of hydroxyl by the sol-gel processing technique. Gels were prepared from optimized amounts of tetraethyl orthosilicate, fumed silica and water. Acids and bases in small quantities were added for catalysing hydrolysis and adjusting the pH. Dried gels were heated up to 1400°C in various atmospheres to obtain transparent silica glass of the required density and very low (<5 ppm) hydroxyl content.     

ITO用作铁电薄膜电极的研究

研究了sol-gel掺锡氧化铟（ITO溶胶在SiO2/Si衬底和光学玻璃衬底上的成膜及结晶性能,并与CVD法生长的ITO薄膜作了对比。结论是：sol-gelITO膜,虽然具有与CVD ITO膜相似的结晶性能和较高的导电性,但以sol-gel ITO膜作下电极,无法使PLT、PZT的sol-gel膜具有明显的结晶取向。因漏电太大,sol-gel ITO也无法作sol-gel铁电膜（如PLT,PZT）的上电极。但在CVD ITO膜上,sol-gel铁电膜能很好结晶,且Au/PLT/ITO电容,具有良好的电学性能。     

ZnO thin films prepared by a single step sol-gel process

ZnO thin films were prepared on fused silica from a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH ] and isopropanol. Crystallization annealing was performed over the range 500 to 650 °C. X-ray analysis showed that thin films were preferentially orientated along the [002] c-axis direction of the crystal. The films had a transparency of greater than 85% in the visible region for sol-gels with a zinc content of up to 0.7 M and exhibited absorption edges at ∼ 378 nm. The optical band-gap energy was evaluated to be 3.298-3.306 eV. Photoluminescence showed a strong emission centered at ca. 380 nm along with a broad yellow-orange emission centered at ca. 610 nm. Single step sol-gel thin film deposition in the film thickness range from 80 nm to 350 nm was demonstrated. The effect of sol-gel zinc concentration, film thickness and crystallization temperature on film microstructure, morphology and optical transparency is detailed. A process window for single spin coating deposition of c-axis oriented ZnO discussed.     

Thickness dependency of sol-gel derived ZnO thin films on gas sensing behaviors

ZnO thin films were fabricated by a sol-gel method using Zn(CH₃COO)₂·2H₂O as starting material in order to prepare an acetone gas sensor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. The sol-gel solution is coated on alumina substrates with various thicknesses by spin coating technique and heat treated to grow crystalline ZnO thin films. The effect of thickness on physical and electrical properties of as deposited ZnO thin films has been studied. The as deposited ZnO thin films were characterized by X-ray diffraction spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The root mean square surface roughness factors increase with thickness of the films and found 3.9, 6.6, 9.0, and 11.28 nm for 80-, 220-, 450- and 620-nm-thin films respectively. The activation energies of the films are calculated from the resistance temperature characteristics. The sensitivities of the ZnO films towards the acetone gas were determined at an operating temperature of 200 °C. The sensitivity towards acetone vapor is strongly depending on surface morphology of the ZnO thin films.     

Phase transformations in TiO2/SiO2 sol-gel films as a function of composition and heat-treatment

The refractive indices of titania/silica sol-gel films are known to vary over a wide range with composition. However, little work has been done to investigate the possible variations in refractive index that can be produced for one specific sol-gel composition by varying the heat-treatment time and temperature. In this study, three different titania/silica sol-gel compositions containing 40, 60 and 80 mol% titania were studied after thermal processing at temperatures from 175–1050°C for variable lengths of time. The refractive indices and thicknesses of the sol-gel films spin-coated on to silicon wafers were determined using a combined technique of ellipsometry and reflectance spectroscopy. The microstructural differences in the films were investigated using X-ray diffraction and transmission electron microscopy techniques.     

溶胶—凝胶方法制备铁电薄膜及其力学性质的研究

本文介绍用溶胶-凝胶方法制备钛酸铅镧(PLT)铁电膜,采用划痕法测定PLT膜在Si基片上的附着力,并通过x射线衍射(XRD)测定在各种工艺条件下PLT薄膜的晶格畸变,并计算内应力。实验表明溶胶-凝胶方法的工艺因素对薄膜的力学性质有很大影响。通过控制溶液浓度,热处理温度及薄膜的厚度可得到附着力强,内应力小,品格畸变小的优质膜。     

Structural Evolution During Reaction to Form Aluminum Titanate from Sol-Gel Precursors

Aluminum titanate ceramic materials have been obtained by field-activated sintering of amorphous sol-gel powder precursors. Aluminum titanate formation started at 1000°C. The structural evolution with temperature from the amorphous sol-gel state to the final fully densified ceramic product has been monitored by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and electron microscopy. The full crystallization of aluminum titanate occurred at 1200°C. The grain size of the specimen densified at 1300°C was between 150 and 500 nm.     

Hydrothermal processing of barium strontium titanate sol-gel composite thin films

Stoichiometric barium strontium titanate (BST) films of composition with thickness >2 μm have been fabricated on Si/SiO₂/Pt substrates by hydrothermal sol-gel composite processing. This film deposition technique involves the treatment of a spun-on sol-gel composite film, formed from a suspension of a powder in an aqueous BST sol-gel, at temperatures from 100–200°C at a pressure of 1–15 atm. An initial hydrolysis procedure eliminates dissolution of the dried sol-gel during the hydrothermal treatment. Glancing angle X-ray diffraction shows excellent crystallinity and stoichiometry in the BST films with no evidence of new phases created during processing. Scanning electron micrography and atomic force microscopy show densification of the film structure and the development of a bridging microstructure. Transmission electron micrography indicates that while much of the sol-gel derived matrix phase is amorphous a more crystalline interface occurs with the powder particles. The relative permittivity and loss tangent of the films are measured using a parallel plate capacitor technique in the frequency range 1–100 kHz. At 100 kHz relative permittivities of the films range from ɛ_r = 400–1200 and loss tangents lie in the range 0.05 < tan δ < 0.10, depending on the parameters of film preparation. The film structure and morphology and the electrical studies suggest that the microstructure of the films evolves by deposition of the sol-gel derived BST on the underlying powder, resulting in an electrically interconnected microstructure in which the sol-gel derived material bridges between the high permittivity powder particles.     

Synthesis, properties and applications of inorganic–organic copolymers (ORMOCERs)

Hybrid inorganic-organic polymers based on organically modified heteropolysiloxanes have found widespread attention and application as materials with adjustable properties using tailor-made precursors. The chemical structures of monomers and their modified sol-gel processing method are described. An overview is given for the control of various properties (mechanical, electrical, optical) of the materials on a molecular scale. Successful material developments and industrial applications are described.